Hello Oliver,
Doing this dialog via the forum involves unnecessary administration and doesn't make much sense to me.
It's like scratching your left ear with your right hand behind your head. It prevents, rather than promotes, distribution of the information to the right people unless all of the right people use the forum, which they don't.
Anyway, the handling of the ILC TPC sectors will be essentially the same as for the Aleph TPC sectors, therefore we must think of this fact and not just of the Eudet situation.
In Aleph we machined trapaziodal oring grooves, small side outside, in "geschnetzeltes GFK from Stesalit" (fibreglass) material, so the complication due to the trapezoid can't be that big of a deal. Also the production of the TPC sectors is not a mass-production operation so it won't be done for thousands or millions of times and a little extra machining work plays a negligible role in the overall effort and timescale. Preventing the orings from falling out during manipulation will be an essential function for the LCTPC sectors.
In Aleph the gas-tightness in fibreglass was ensured by using a thin coating of vacuum grease on the orings. Also 2-surface contact was entirely adequate for 6mbar overpressure (in the LCTPC it will be 2mbar). Since the Aleph TPC worked extremely well during 12 years of operation, we don't have to do too much of "reinvention of the wheel", although we should of course think of improvements since the Aleph TPC was not perfect...
Cheers,
Ron